Field studies of film slicks in shear currents

Stanislav Ermakov, Irina Sergievskaya, Yury Shchegolkov, Lev Gushin, Eugeny Makarov
Institute of Applied Physics, Russian Academy of Sciences
Nizhny Novgorod, 603950, Russia
stas.ermakov@hydro.appl.sci-nnov.ru

ABSTRACT

Natural slicks on the sea surface are often formed due to an accumulation of surfactants by surface currents associated with different dynamical processes in the ocean and the atmosphere, and, therefore, can be considered as indicators of these processes. At present, however, there are only few observations of slick formation due to oceanic/atmospheric phenomena, including some observations of banded slicks associated with internal waves and one experiment where a film slick was studied simultaneously with ocean currents (see, Ermakov et.al., Manifestations of a current gradient on the sea surface in the presence of a surfactant film, in The Air-Sea Interface. Radio and Acoustic Sensing, Turbulence and Wave Dynamics, Univ.Toronto Press Inc., Toronto, 395-400, 1993). In the latter, however, the current measurements were conducted in a layer of about 10m depth, so that does not give a direct proof of formation of slicks by inhomogeneous currents. One should note that measuring of surface velocities is a difficult problem, which can partly explain that mechanisms of slick formation are still not well understood. In this work a new methodology of measurements of velocities in a thin surface water layer (the thickness of about 5 mm) is proposed and used to measure a structure of surface currents near boundaries of film slicks. Experiments were carried out in the coastal zone of the Black Sea in August, 2004. The methodology of measuring surface velocities is based on the use of GPS receivers and floating markers. Film sampling from banded slicks was carried out simultaneously with current measurements and the studied slicks were shown to be associated with accumulation of surfactants. The damping coefficient of capillary-gravity waves measured for the film samples was obtained to be several times larger in slick zones than in surrounding non-slick areas. The slicks were shown to be located in the shear current zones, and transverse current components in the shear zones directed towards the slick boundaries were detected.

The work was supported by INTAS (Project 03-51-4987, “SIMP”) and RFBR (Projects 02-05-65102, 04-05-64763, 05-05-64137).

Last Update: 2005-03-16